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## Exercise 3.1 Page: 44

**1. Aftab tells his daughter, “Seven years ago, I was seven times as old as you were then. Also, three years from now, I shall be three times as old as you will be.” (Isn’t this interesting?) Represent this situation algebraically and graphically.**

**Solutions: **Let the present age of Aftab be ‘x’.

And, the present age of his daughter be ‘y’.

Now, we can write, seven years ago,

Age of Aftab = x – 7

Age of his daughter = y – 7

According to the question,

x−7 = 7(y−7)

⇒ x−7 = 7y−49

⇒ x−7y = −42 ………………………(i)

Also, three years from now or after three years,

Age of Aftab will become = x + 3.

Age of his daughter will become = y + 3

According to the situation given,

x+3 = 3(y+3)

⇒x+3 = 3y+9

⇒x−3y = 6 …………..…………………(ii)

Subtracting equation (i) from equation (ii) we have

(x−3y)−(x−7y) = 6−(−42)

⇒−3y+7y=6+42

⇒4y=48

⇒y=12

The algebraic equation is represented by

x−7y = −42

x−3y = 6

For, x−7y =−42 or x = −42+7y

The solution table is

For, x−3y=6 or x=6+3y

The solution table is

The graphical representation is:

**2. The coach of a cricket team buys 3 bats and 6 balls for Rs.3900. Later, she buys another bat and 3 more balls of the same kind for Rs.1300. Represent this situation algebraically and geometrically.**

**Solutions: **Let us assume that the cost of a bat be ‘Rs x’

And,the cost of a ball be ‘Rs y’

According to the question, the algebraic representation is

3x+6y=3900

and x+2y=1300

For, 3x+6y=3900

Or x=

The solution table is

x |
300 |
100 |
-100 |

y |
500 |
600 |
700 |

For, x+2y=1300

Or x=1300-2y

The solution table is

x |
300 |
100 |
-100 |

y |
500 |
600 |
700 |

The graphical representation is as follows.

**3. The cost of 2 kg of apples and 1kg of grapes on a day was found to be Rs.160. After a month, the cost of 4 kg of apples and 2 kg of grapes is Rs.300. Represent the situation algebraically and geometrically.**

**Solutions: **Let the cost of 1 kg of apples be ‘Rs. x’

And, cost of 1 kg of grapes be ‘Rs. y’

According to the question, the algebraic representation is

2x+y=160

And 4x+2y=300

For, 2x+y=160 or y=160−2x, the solution table is;

x |
50 |
60 |
70 |

y |
60 |
40 |
20 |

For 4x+2y=300 or y = , the solution table is;

x |
70 |
80 |
75 |

y |
10 |
-10 |
0 |

The graphical representation is as follows;

## Exercise 3.2 Page: 49

**1. Form the pair of linear equations in the following problems, and find their solutions graphically. **

**(i) 10 students of Class X took part in a Mathematics quiz. If the number of girls is 4 more than the number of boys, find the number of boys and girls who took part in the quiz. **

**(ii) 5 pencils and 7 pens together cost ` 50, whereas 7 pencils and 5 pens together cost ` 46. Find the cost of one pencil and that of one pen.**

**Solution:**

(i) Let there are x number of girls and y number of boys. As per the given question, the algebraic expression can be represented as follows.

x + y = 10

x – y = 4

Now, for x + y = 10 or x=10−y, the solutions are;

x |
5 |
4 |
6 |

y |
5 |
6 |
4 |

For x – y = 4 or x = 4 + y, the solutions are;

x |
4 |
5 |
3 |

y |
0 |
1 |
-1 |

The graphical representation is as follows;

**From the graph, it can be seen that the given lines cross each other at point (7, 3). Therefore, there are 7 girls and 3 boys in the class.**

**(ii) **Let 1 pencil costs Rs.x and 1 pen costs Rs.y.

According to the question, the algebraic expression cab be represented as;

5x + 7y = 50

7x + 5y = 46

For, 5x + 7y = 50 or x =, the solutions are;

x |
3 |
10 |
-4 |

y |
5 |
0 |
10 |

**For **7x + 5y = 46 or x =, the solutions are;

x |
8 |
3 |
-2 |

y |
-2 |
5 |
12 |

Hence, the graphical representation is as follows;

From the graph, it is can be seen that the given lines cross each other at point (3, 5).

So, the cost of a eraser is 3/- and cost of a chocolate is 5/-.

**2. On comparing the ratios , find out whether the lines representing the following pairs of linear equations intersect at a point, are parallel or coincident: **

**(i) 5x – 4y + 8 = 0**

** 7x + 6y – 9 = 0 **

**(ii) 9x + 3y + 12 = 0**

** 18x + 6y + 24 = 0 **

**(iii) 6x – 3y + 10 = 0**

** 2x – y + 9 = 0**

**Solutions:**

(i) Given expressions;

**5x−4y+8=0**

**7x+6y−9=0**

Comparing these equations with x + y + =0

And x + y + = 0

So, the pairs of equations given in the question have a unique solution and the lines cross each other at exactly one point.

(ii) Given expressions;

**9x + 3y + 12 = 0**

**18x + 6y + 24 = 0 **

Comparing these equations with x + y + =0

And x + y + = 0

We get,

So, the pairs of equations given in the question have infinite possible solutions and the lines are coincident.

(iii) Given Expressions;

**6x – 3y + 10 = 0**

**2x – y + 9 = 0**

So, the pairs of equations given in the question are parallel to each other and the lines never intersect each other at any point and there is no possible solution for the given pair of equations.

**3. On comparing the ratios , find out whether the following pair of linear equations are consistent, or inconsistent. **

**(i) 3x + 2y = 5 ; 2x – 3y = 7 **

**(ii) 2x – 3y = 8 ; 4x – 6y = 9 **

**(iii); 9x – 10y = 14 **

**(iv) 5x – 3y = 11 ; – 10x + 6y = –22 **

**(v) ; 2x + 3y = 12**

**Solutions: **

**(i) Given : 3x + 2y = 5 or 3x + 2y -5 = 0**

**and 2x – 3y = 7 or 2x – 3y -7 = 0 **

**(ii) Given 2x – 3y = 8 and 4x – 6y = 9 **

**Therefore,**

**(iii) and 9x – 10y = 14 **

**Therefore,**

So, the equations are intersecting each other at one point and they have only one possible solution. Hence, the equations are consistent.

**(iv) Given, 5x – 3y = 11 and – 10x + 6y = –22 **

**Therefore, **

**(v) and 2x + 3y = 12**

**4. Which of the following pairs of linear equations are consistent/inconsistent? If consistent, obtain the solution graphically:**

**(i) x + y = 5, 2x + 2y = 10 **

**(ii) x – y = 8, 3x – 3y = 16 **

**(iii) 2x + y – 6 = 0, 4x – 2y – 4 = 0 **

**(iv) 2x – 2y – 2 = 0, 4x – 4y – 5 = 0**

**Solutions:**

**(i) Given, x + y = 5 and 2x + 2y = 10**

So, the equations are represented in graphs as follows:

From the figure, we can see, that the lines are overlapping each other.

Therefore, the equations have infinite possible solutions.

**(ii) Given, x – y = 8 and 3x – 3y = 16 **

**(iii) Given, 2x + y – 6 = 0 and 4x – 2y – 4 = 0 **

From the graph, it can be seen that these lines are intersecting each other at only one point,(2,2).

**(iv) Given, 2x – 2y – 2 = 0 and 4x – 4y – 5 = 0**

Thus, these linear equations have parallel and have no possible solutions. Hence, the pair of linear equations are inconsistent.

**5. Half the perimeter of a rectangular garden, whose length is 4 m more than its width, is 36 m. Find the dimensions of the garden.**

**Solutions: **Let us consider.

The width of the garden is x and length is y.

Now, according to the question, we can express the given condition as;

y – x = 4

and

y + x = 36

Now, taking y – x = 4 or y = x + 4

x |
0 |
8 |
12 |

y |
4 |
12 |
16 |

For ** **y + x = 36, y = 36 – x

x |
0 |
36 |
36 |

y |
36 |
0 |
20 |

The graphical representation of both the equation is as follows;

From the graph you can see, the lines intersects each other at a point(16, 20). Hence, the width of the garden is 16 and length is 20.

**6. Given the linear equation 2x + 3y – 8 = 0, write another linear equation in two variables such that the geometrical representation of the pair so formed is: **

**(i) Intersecting lines **

**(ii) Parallel lines **

**(iii) Coincident lines**

**Solutions:**

**(i) Given the linear equation 2x + 3y – 8 = 0.**

To find another linear equation in two variables such that the geometrical representation of the pair so formed is intersecting lines, it should satisfy below condition;

Clearly, you can see another equation satisfies the condition.

**(ii) Given the linear equation 2x + 3y – 8 = 0.**

To find another linear equation in two variables such that the geometrical representation of the pair so formed is parallel lines, it should satisfy below condition;

Clearly, you can see another equation satisfies the condition.

**(iii) Given the linear equation 2x + 3y – 8 = 0.**

To find another linear equation in two variables such that the geometrical representation of the pair so formed is coincident lines, it should satisfy below condition;

Clearly, you can see another equation satisfies the condition.

**7. Draw the graphs of the equations x – y + 1 = 0 and 3x + 2y – 12 = 0. Determine the coordinates of the vertices of the triangle formed by these lines and the x-axis, and shade the triangular region.**

**Solution: Given, the equations for graphs are x – y + 1 = 0 and 3x + 2y – 12 = 0.**

**For, x – y + 1 = 0 or x = 1+y**

x |
0 |
1 |
2 |

y |
1 |
2 |
3 |

**For, 3x + 2y – 12 = 0 or x = **

x |
4 |
2 |
0 |

y |
0 |
3 |
6 |

Hence, the graphical representation of these equations is as follows;

From the figure, it can be seen that these lines are intersecting each other at point (2, 3) and x-axis at (−1, 0) and (4, 0). Therefore, the vertices of the triangle are (2, 3), (−1, 0), and (4, 0).

## Exercise 3.3 Page: 53

**1. Solve the following pair of linear equations by the substitution method**

**(i) x + y = 14**

** x – y = 4**

**(ii) s – t = 3**

** **

**(iii) 3x – y = 3**

** 9x – 3y = 9**

**(iv) 0.2x + 0.3y = 1.3 **

** 0.4x + 0.5y = 2.3**

**(v) **

** **

**(vi) **

** **

**Solutions:**

**(i) Given, **

** x + y = 14 and x – y = 4 are the two equations.**

From 1^{st} equation, we get,

x = 14 – y

Now, substitute the value of x in second equation to get,

(14 – y) – y = 4

14 – 2y = 4

2y = 10

Or y = 5

By the value of y, we can now find the exact value of x;

∵ x = 14 – y

∴ x = 14 – 5

Or x = 9

**Hence, x = 9 and y = 5.**

**(ii) Given, **

**(iii) Given, **

**(iv) Given,**

**(v) Given,**

**(vi) Given,**

**2. Solve 2x + 3y = 11 and 2x – 4y = – 24 and hence find the value of ‘m’ for which y = mx + 3.**

**Solutions: **

**3. Form the pair of linear equations for the following problems and find their solution by substitution method.**

**(i) The difference between two numbers is 26 and one number is three times the other. Find them.**

**Solutions:**

Let the two numbers be x and y respectively, such that y > x.

According to the question,

y = 3x ……………… (1)

y – x = 26 …………..(2)

Substituting the value of (1) into (2), we get

3x – x = 26

x = 13 ……………. (3)

Substituting (3) in (1), we get y = 39

**Hence, the numbers are 13 and 39.**

**(ii) The larger of two supplementary angles exceeds the smaller by 18 degrees. Find them.**

**Solutions:**

Let the larger angle by x^{o} and smaller angle be y^{o}.

We know that the sum of two supplementary pair of angles is always 180^{o}.

According to the question,

x + y = 180^{o}……………. (1)

x – y = 18^{o }……………..(2)

From (1), we get x = 180^{o} – y …………. (3)

Substituting (3) in (2), we get

180^{o }– y – y =18^{o}

162^{o} = 2y

y = 81^{o} ………….. (4)

Using the value of y in (3), we get

x = 180^{o} – 81^{o}

= 99^{o}

**Hence, the angles are 99 ^{o} and 81^{o}.**

**(iii) The coach of a cricket team buys 7 bats and 6 balls for Rs.3800. Later, she buys 3 bats and 5 balls for Rs.1750. Find the cost of each bat and each ball.**

**Solutions:**

**(iv) The taxi charges in a city consist of a fixed charge together with the charge for the distance covered. For a distance of 10 km, the charge paid is ` 105 and for a journey of 15 km, the charge paid is ` 155. What are the fixed charges and the charge per km? How much does a person have to pay for travelling a distance of 25 km?**

**Solution:**

Let the fixed charge be Rs x and per km charge be Rs y.

According to the question,

x + 10y = 105 …………….. (1)

x + 15y = 155 …………….. (2)

From (1), we get x = 105 – 10y ………………. (3)

Substituting the value of x in (2), we get

105 – 10y + 15y = 155

5y = 50

y = 10 …………….. (4)

Putting the value of y in (3), we get

x = 105 – 10 × 10 = 5

**Hence, fixed charge is Rs 5 and per km charge = Rs 10**

**Charge for 25 km = x + 25y = 5 + 250 = Rs 255**

**(v) A fraction becomes , if 2 is added to both the numerator and the denominator. If, 3 is added to both the numerator and the denominator it becomes . Find the fraction.**

**Solution:**

** **

**(vi) Five years hence, the age of Jacob will be three times that of his son. Five years ago, Jacob’s age was seven times that of his son. What are their present ages?**

**Solutions:**

Let the age of Jacob and his son be x and y respectively.

According to the question,

(x + 5) = 3(y + 5)

x – 3y = 10 …………………………………….. (1)

(x – 5) = 7(y – 5)

x – 7y = -30 ………………………………………. (2)

From (1), we get x = 3y + 10 ……………………. (3)

Substituting the value of x in (2), we get

3y + 10 – 7y = -30

-4y = -40

y = 10 ………………… (4)

Substituting the value of y in (3), we get

x = 3 x 10 + 10 = 40

**Hence, the present age of Jacob’s and his son is 40 years and 10 years respectively.**

## Exercise 3.4 Page: 56

**1. Solve the following pair of linear equations by the elimination method and the substitution method:**

**(i) x + y = 5 and 2x – 3y = 4**

**(ii) 3x + 4y = 10 and 2x – 2y = 2**

**(iii) 3x – 5y – 4 = 0 and 9x = 2y + 7**

**(iv) **

**Solutions:**

**(i) x + y = 5 and 2x – 3y = 4**

** **

**(ii) 3x + 4y = 10 and 2x – 2y = 2**

**By the method of elimination.**

3x + 4y = 10……………………….(i)

2x – 2y = 2 ………………………. (ii)

When the equation (i) and (ii) is multiplied by 2, we get:

4x – 4y = 4 ………………………..(iii)

When the Equation (i) and (iii) are added, we get:

7x = 14

x = 2 ……………………………….(iv)

Substituting equation (iv) in (i) we get,

6 + 4y = 10

4y = 4

y = 1

**Hence, x = 2 and y = 1**

**By the method of Substitution**

From equation (ii) we get,

x = 1 + y……………………………… (v)

Substituting equation (v) in equation (i) we get,

3(1 + y) + 4y = 10

7y = 7

y = 1

When y = 1 is substituted in equation (v) we get,

A = 1 + 1 = 2

**Therefore, A = 2 and B = 1**

**(iii) 3x – 5y – 4 = 0 and 9x = 2y + 7**

**By the method of elimination:**

**(iv) **

**2. Form the pair of linear equations in the following problems, and find their solutions (if they exist) by the elimination method:**

**(i) If we add 1 to the numerator and subtract 1 from the denominator, a fraction reduces to 1. It becomes if we only add 1 to the denominator. What is the fraction?**

**Solutions:**

Let the fraction be a/b

According to the given information,

When equation (i) is subtracted from equation (ii) we get,

a = 3 …………………………………………………..(iii)

When a = 3 is substituted in equation (i) we get,

3 – b = -2

-b = -5

b = 5

**Hence, the fraction is 3/5.**

**(ii) Five years ago, Nuri was thrice as old as Sonu. Ten years later, Nuri will be twice as old as Sonu. How old are Nuri and Sonu?**

**Solutions:**

Let us assume, present age of Nuri is x

And present age of Sonu is y.

According to the given condition, we can write as;

x – 5 = 3(y – 5)

x – 3y = -10…………………………………..(1)

Now,

x + 10 = 2(y +10)

x – 2y = 10…………………………………….(2)

Subtract eq. 1 from 2, to get,

y = 20 ………………………………………….(3)

Substituting the value of y in eq.1, we get,

x – 3.20 = -10

x – 60 = -10

x = 50

Therefore,

Age of Nuri is 50 years

Age of Sonu is 20 years.

**(iii) The sum of the digits of a two-digit number is 9. Also, nine times this number is twice the number obtained by reversing the order of the digits. Find the number.**

**Solutions:** Let the unit digit and tens digit of a number be x and y respectively.

Then, Number (n) = 10B + A

N after reversing order of the digits = 10A + B

According to the given information, A + B = 9…………………….(i)

9(10B + A) = 2(10A + B)

88 B – 11 A = 0

-A + 8B = 0 ………………………………………………………….. (ii)

Adding the equations (i) and (ii) we get,

9B = 9

B = 1……………………………………………………………………….(3)

Substituting this value of B, in the equation (i) we get A= 8

**Hence the number (N) is 10B + A = 10 x 1 +8 = 18**

**(iv) Meena went to a bank to withdraw Rs.2000. She asked the cashier to give her Rs.50 and Rs.100 notes only. Meena got 25 notes in all. Find how many notes of Rs.50 and Rs.100 she received.**

**Solutions: **Let the number of Rs.50 notes be A and the number of Rs.100 notes be B

According to the given information,

A + B = 25 ……………………………………………………………………….. (i)

50A + 100B = 2000 ………………………………………………………………(ii)

When equation (i) is multiplied with (ii) we get,

50A + 50B = 1250 …………………………………………………………………..(iii)

Subtracting the equation (iii) from the equation (ii) we get,

50B = 750

B = 15

Substituting in the equation (i) we get,

A = 10

**Hence, Manna has 10 notes of Rs.50 and 15 notes of Rs.100.**

**(v) A lending library has a fixed charge for the first three days and an additional charge for each day thereafter. Saritha paid Rs.27 for a book kept for seven days, while Susy paid Rs.21 for the book she kept for five days. Find the fixed charge and the charge for each extra day.**

**Solutions:** Let the fixed charge for the first three days be Rs.A and the charge for each day extra be Rs.B.

According to the information given,

A + 4B = 27 …………………………………….…………………………. (i)

A + 2B = 21 ……………………………………………………………….. (ii)

When equation (ii) is subtracted from equation (i) we get,

2B = 6

B = 3 …………………………………………………………………………(iii)

Substituting B = 3 in equation (i) we get,

A + 12 = 27

A = 15

**Hence, the fixed charge is Rs.15/-**

**And the Charge per day is Rs.3/-.**

## Exercise 3.5 Page: 62

**1. Which of the following pairs of linear equations has unique solution, no solution, or infinitely many solutions. In case there is a unique solution, find it by using cross multiplication method.**

**(i) x – 3y – 3 = 0 and 3x – 9y – 2 = 0 (ii) 2x + y = 5 and 3x + 2y = 8**

**(iii) 3x – 5y = 20 and 6x – 10y = 40 (iv) x – 3y – 7 = 0 and 3x – 3y – 15 = 0**

Solutions:

**2. (i) For which values of a and b does the following pair of linear equations have an infinite number of solutions? **

**3y + 2x = 7**

**(a – b) x + (a + b) y = 3a + b – 2 **

**(ii) For which value of k will the following pair of linear equations have no solution? **

**3x + y = 1 **

**(2k – 1) x + (k – 1) y = 2k + 1**

**Solution:**

**3. Solve the following pair of linear equations by the substitution and cross-multiplication methods: **

**8x + 5y = 9 **

**3x + 2y = 4**

**Solution:**

8x + 5y = 9 …………………..(1)

3x + 2y = 4 ……………….….(2)

From equation (2) we get

x = 4 – 2y / 3 ……………………. (3)

Using this value in equation 1, we get

8(4-2y)/3 + 5y = 9

32 – 16y +15y = 27

-y = -5

y = 5 ……………………………….(4)

Using this value in equation (2), we get

3x + 10 = 4

x = -2

Thus, x = -2 and y = 5.

Now, Using Cross Multiplication method:

8x +5y – 9 = 0

3x + 2y – 4 = 0

x/(-20+18) = y/(-27 + 32 ) = 1/(16-15)

-x/2 = y/5 =1/1

∴ x = -2 and y =5.

**4. Form the pair of linear equations in the following problems and find their solutions (if they exist) by any algebraic method:**

**(i) A part of monthly hostel charges is fixed and the remaining depends on the number of days one has taken food in the mess. When a student A takes food for 20 days she has to pay Rs.1000 as hostel charges whereas a student B, who takes food for 26 days, pays Rs.1180 as hostel charges. Find the fixed charges and the cost of food per day. **

**(ii) A fraction becomes 1/3 when 1 is subtracted from the numerator and it becomes 1/4 when 8 is added to its denominator. Find the fraction. **

**(iii) Yash scored 40 marks in a test, getting 3 marks for each right answer and losing 1 mark for each wrong answer. Had 4 marks been awarded for each correct answer and 2 marks been deducted for each incorrect answer, then Yash would have scored 50 marks. How many questions were there in the test? **

**(iv) Places A and B are 100 km apart on a highway. One car starts from A and another from B at the same time. If the cars travel in the same direction at different speeds, they meet in 5 hours. If they travel towards each other, they meet in 1 hour. What are the speeds of the two cars? **

**(v) The area of a rectangle gets reduced by 9 square units, if its length is reduced by 5 units and breadth is increased by 3 units. If we increase the length by 3 units and the breadth by 2 units, the area increases by 67 square units. Find the dimensions of the rectangle.**

Solutions:

**(i)** Let x be the fixed charge and y be the charge of food per day.

According to the question,

x + 20y = 1000……………….. (i)

x + 26y = 1180………………..(ii)

Subtracting (i) from (ii) we get

6y = 180

y = Rs.30

Using this value in equation (ii) we get

x = 1180 -26 x 30

x= Rs.400.

Therefore, fixed charges is Rs.400 and charge per day is Rs.30.

**(ii) **L*et* the fraction be x/y.

So, as per the question given,

(x -1)/y = 1/3 => 3x – y = 3…………………(1)

x/(y + 8) = 1/4 => 4x –y =8 ………………..(2)

Subtracting equation (1) from (2) , we get

x = 5 ………………………………………….(3)

Using this value in equation (2), we get,

4×5 – y = 8

y= 12

Therefore, the fraction is 5/12.

**(iv)** Let x be the number of correct numbers and y be the number of incorrect answers.

According to the question given,

3x – y = 40 …………………………………(i)

4x – 2y = 50

And 2x-y = 25………………………………(ii)

Subtracting equation (ii) from (i), we get

x=15………………………………………(iii)

Using this in equation (i), we get,

3(15) – 40 = y

y= 5

Therefore, the number of correct answers = 15

And the number of incorrect answers = 5

The total number of questions =20

(v) Let,

The length of rectangle = x unit

And breadth of the rectangle = y unit

Now, as per the question given,

(x – 5) (y + 3) = xy -9

3x – 5y – 6 = 0……………………………(1)

(x + 3) (y + 2) = xy + 67

2x + 3y – 61 = 0…………………………..(2)

Using cross multiplication method, we get,

Therefore, x = 17 and y = 9.

Hence, the length of rectangle = 17 units

And breadth of the rectangle = 9 units

## Exercise 3.6 Page: 67

**1. Solve the following pairs of equations by reducing them to a pair of linear equations:**

**(i) **

** **

**(ii) = 2**

** **

(iii)

**(iv) **

**(v)**

** **

**(vi) 6x + 3y = 6xy**

**2x + 4y = 5xy**

** (vii) **

**Solution:**

(viii)

**2. Formulate the following problems as a pair of equations, and hence find their solutions: **

**(i) Ritu can row downstream 20 km in 2 hours, and upstream 4 km in 2 hours. Find her speed of rowing in still water and the speed of the current. **

**(ii) 2 women and 5 men can together finish an embroidery work in 4 days, while 3 women and 6 men can finish it in 3 days. Find the time taken by 1 woman alone to finish the work, and also that taken by 1 man alone. **

**(iii) Roohi travels 300 km to her home partly by train and partly by bus. She takes 4 hours if she travels 60 km by train and the remaining by bus. If she travels 100 km by train and the remaining by bus, she takes 10 minutes longer. Find the speed of the train and the bus separately.**

**Solutions:**

- Let us consider,

Speed of Ritu is still water = x km/hr

Speed of Stream = y km/hr

Now, speed of Ritu, during,

Downstream = x + y km/h

Upstream = x – y km/h

As per the question given,

2(x+y) = 20

Or x + y = 10……………………….(1)

And, 2(x-y) = 4

Or x – y = 2………………………(2)

Adding both the eq.1 and 2, we get,

2x=12

x = 6

Putting the value of x in eq.1, we get,

y = 4

Therefore,

Speed of Ritu is still water = 6 km/hr

Speed of Stream = 4 km/hr

- Let us consider,

Number of days taken by women to finish the work = x

Number of days taken by men to finish the work = y

Work done by women in one day = 1/x

Work done by women in one day = 1/y

As per the question given,

- Let us consider,

Speed of the train = x km/h

Speed of the bus = y km/h

## Exercise 3.7 Page: 68

**1. The ages of two friends Ani and Biju differ by 3 years. Ani’s father Dharam is twice as old as Ani and Biju is twice as old as his sister Cathy. The ages of Cathy and Dharam differ by 30 years. Find the ages of Ani and Biju.**

Solutions: The age difference between Ani and Biju** **is 3 yrs.

Either Biju is 3 years older than that of Ani or Ani is 3 years older than Biju. From both the cases we find out that Ani’s father’s age is 30 yrs more than that of Cathy’s age.

Let the ages of Ani and Biju** **be A and B respectively.

Therefore, the age of Dharam = 2 x A = 2A yrs.

And the age of Biju sister Ann B/2 yrs

By using the information that is given,

Case (i)

When Ani is older than that of Biju by 3 yrs then A – B = 3 – – – – – – – – (1)

2A−B2=30

4A – B = 60 – – – – – – – – – – – (2)

By subtracting the equations (1) and (2) we get,

3A = 60 – 3 = 57

A= 57/3 =19

Therefore, the age of Ani = 19 yrs

And the age of Biju is 19 – 3 = 16 yrs.

Case (ii)

When Biju is older than Ani,

B – A = 3 – – – – – – – – – (1)

2A−Y/2=30

4A – B = 60 – – – – – – – – – (2)

Adding the equation (1) and (2) we get,

3A = 63

A = 21

Therefore, the age of Ani is 21 yrs

And the age of Biju is 21 + 3 = 24 yrs.

**2. One says, “Give me a hundred, friend! I shall then become twice as rich as you”. The other replies, “If you give me ten, I shall be six times as rich as you”. Tell me what is the amount of their (respective) capital? [From the Bijaganita of Bhaskara II] [Hint : x + 100 = 2(y – 100), y + 10 = 6(x – 10)].**

Solutions: Let Sangam have Rs A with him and Reuben have Rs B with him.

Using the information that is given we get,

A + 100 = 2(B – 100) A + 100 = 2B – 200

Or A – 2B = -300 – – – – – – – (1)

And

6(A – 10) = ( B + 10 )

Or 6A – 60 = B + 10

Or 6A – B = 70 – – – – – – (2)

When equation (2) is multiplied by 2 we get,

12A – 2B = 140 – – – – – – – (3)

When equation (1) is subtracted from equation (3) we get,

11A = 140 + 300

11A = 440A

=> 40

Using A =40 in equation (1) we get,

40 – 2B = -300

40 + 300 = 2B

2B = 340

B = 170

Therefore, Sangam had Rs 40 and Reuben had Rs 170 with them.

**3. A train covered a certain distance at a uniform speed. If the train would have been 10 km/h faster, it would have taken 2 hours less than the scheduled time. And, if the train were slower by 10 km/h; it would have taken 3 hours more than the scheduled time. Find the distance covered by the train.**

**4. The students of a class are made to stand in rows. If 3 students are extra in a row, there would be 1 row less. If 3 students are less in a row, there would be 2 rows more. Find the number of students in the class.**

**Solution:**

Let the number of rows be A and the number of students in a row be B.

Total number of students = Number of rows x Number of students in a row

=AB

Using the information, that is given,

**First Condition:**

Total number of students = (A – 1) ( B + 3)

Or AB = ( A – 1 )(B + 3) = AB – B + 3A – 3

Or 3A – B – 3 = 0

Or 3A – Y = 3 – – – – – – – – – – – – – (1)

**Second condition:**

Total Number of students = (A + 2 ) ( B – 3 )

Or AB = AB + 2B – 3A – 6

Or 3A – 2B = -6 – – – – – – – – – (2)

When equation (2) is subtracted from (1)

(3A – B) – (3A – 2B) = 3 – (-6)

-B + 2B = 3 + 6B = 9

By using the equation (1) we get,

3A – 9 =3

3A = 9+3 = 12

A = 4

Number of rows, A = 4

Number of students in a row, B = 9

Number of total students in a class => AB => 4 x 9 = 36

**5. In a ∆ABC, ∠ C = 3 ∠ B = 2 (∠A + ∠ B). Find the three angles.**

**Solution:**

**6. Draw the graphs of the equations 5x – y = 5 and 3x – y = 3. Determine the co-ordinates of the vertices of the triangle formed by these lines and the y axis.**

**Solutions: Given, **

5x – y = 5

=> y =5x – 5

Its solution table will be.

x |
2 |
1 |
0 |

y |
5 |
0 |
-5 |

Also given,3x – y = 3

y = 3x – 3

x |
2 |
1 |
0 |

y |
3 |
0 |
-3 |

The graphical representation of these lines will be as follows:

From the above graph we can see that the triangle formed is ∆ABC by the lines and the y axis. Also the coordinates of the vertices are A(1,0) , C(0,-5) and B(0,-3).

**7. Solve the following pair of linear equations:**

**(i) px + qy = p – q**

**qx – py = p + q**

**(ii) ax + by = c**

**bx + ay = 1 + c**

**(iii) x/a – y/b = 0**

**ax + by = a ^{2} + b^{2}**

**(iv) (a – b)x + (a + b) y = a ^{2} – 2ab – b^{2}**

**(a + b)(x + y) = a ^{2} + b^{2}**

**(v) 152x – 378y = – 74**

** –378x + 152y = – 604**

**Solutions:**

8. ABCD is a cyclic quadrilateral (see Fig. 3.7). Find the angles of the cyclic quadrilateral.

**Solutions:** It is known that the sum of the opposite angles of a cyclic quadrilateral is 180^{o}

Thus, we have

## NCERT Solutions for Class 10 Maths Chapter 3- Pair of Linear Equations in Two Variables

Chapter 3- Pair of Linear Equations in Two Variables holds a weightage of 11 marks in the examinations. The question paper of the year 2018 had 11 marks questions asked. This chapter gives an account of the various topics related to the linear equations in two variables. The topics discussed in the chapter are mentioned below:

3.1 Introduction

3.2 Pair of Linear Equations in Two Variables

3.3 Graphical Method of Solution of a pair of Linear Equations

3.4 Algebraic Methods of Solving a Pair of Linear Equations

3.5 Equations Reducible to a Pair of Linear Equation in Two Variables

List of Exercises

Exercise 3.1 Solutions– 3 Questions

Exercise 3.2 Solutions– 7 Questions

Exercise 3.3 Solutions– 3 Questions

Exercise 3.4 Solutions– 2 Questions

Exercise 3.5 Solutions– 4 Questions

Exercise 3.6 Solutions– 2 Questions

Exercise 3.7 Solutions– 8 Questions

## NCERT Solutions for Class 10 Maths Chapter3- Pair of Linear Equations in Two Variables

Chapter 3 Pair of Linear Equations in Two Variables explains all about the pair of linear equations in two variables. Two linear equations in the same two variables are called pair of linear equations in two variables. It can be represented graphically and algebrically.

The **graph** can be represented by two lines:

- If the lines intersect at a point, the pair of equations is said to be consistent.
- If the lines coincide, the pair of equations is dependent.
- If the lines are parallel, the pair of equations is inconsistent.

**Algebraically **the following methods can be used to solve the pair of linear equations in two variables:

- Substitution method
- Elimination method
- Cross-multiplication method

### Key Features of NCERT Solutions Class 10 Maths Chapter 3- Pair of Linear Equations in Two Variables

- NCERT Solutions is created by subject experts.
- The answers are provided after a lot of brainstorming and are accurate.
- These contain questions related to all the important topics.
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